In recent years, expectation for electric vehicles or hybrid electric vehicles has increased because of the global environmental problems. For rechargeable batteries as the power supply of those vehicles, both reduction in the size and weight and increase of the capacity and output are demanded. Thus, a battery pack in which a plurality of batteries formed by cells are connected in series is used as the power supply. Moreover, a battery pack in which, in order to cool respective batteries, the batteries are arranged in parallel in an outer case and a cool air from the vehicle interior is introduced by a fan into the outer case is known from Japanese Patent Laid-Open Publication No. 2001-319697, for example.
In such a structure, when any trouble occurs in the battery and gas is discharged from the battery via a gas-discharge port provided in the battery, that gas collects in the outer case. That collecting gas may flow back to the vehicle interior while the fan stops.
In order to solve this problem of the collecting gas, Japanese Patent Laid-Open Publication No. 10-255735 discloses a battery pack in which a plurality of hollow bulkheads are provided for supporting the batteries while the gas-discharge ports provided on end faces of the respective batteries are arranged in an inner space. The gas discharged from the battery is discharged to the outside of the vehicle through an exhaust tube connected to each bulkhead.
However, the structures mentioned above have the following problems. First, in the structure disclosed in Japanese Patent Laid-Open Publication No. 2001-319697, the number of the batteries provided in the outer case is fixed. Therefore, in order to deal with various output voltages, it is necessary to change the specification of the outer case, thus increasing the cost. Moreover, as described above, the gas discharged from the battery when the battery falls into abnormal state is not discharged to the outside of the vehicle without fail.
In the structure disclosed in Japanese Patent Laid-Open Publication No. 10-255735, in order to cool the batteries, it is necessary to place the batteries in the outer case while the bulkheads support the respective batteries and to provide an air-blow chamber and an exhaust chamber so as to allow the cool air to flow in the surrounding of each battery between the bulkheads. In addition, in order to deal with various output voltages, it is necessary to change the specification of the bulkhead, the outer case or the chamber. Furthermore, it is necessary to connect the exhaust tube to each of the bulkheads. Thus, the structure is complicated and the number of parts of the structure is large, increasing the cost.
Therefore, the present invention was made in view of the aforementioned problems of the conventional techniques, and aims to provide a battery pack and a holding frame used in that battery pack, which enable effective cooling of each battery, allow the battery pack having a desired output voltage to be easily formed, is easy and reliable to assemble, provides a simple structure at a low cost, and surely separates and discharges gas discharged from the battery in the battery pack when the battery falls into abnormal state.